Particular embodiments generally relate to dimming of electronic devices.
Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
A dimmer, which includes a triode for alternating current (TRIAC), is used for dimming of incandescent lamps. The dimmer may use forward or reverse phase control. Both phase control schemes chop an alternating current (AC) line voltage either at the beginning of the half sine waveform (forward phase control) or at the end of the half sine waveform (reverse phase control). This stops the power delivered to the incandescent lamp for an adjustable/controllable part of the sine waveform, which is referred to as a non-conduction angle. The ratio between the conduction portion and the full waveform defines the dimming level.
The above type of dimming uses the characteristics of the TRIAC. For example, the TRIAC can be turned on at a controlled moment and after that, the TRIAC stays in full conduction until the current through the TRIAC goes under a sustaining level in either direction. For example, when the sine waveform crosses zero, the current goes below the sustaining level and the TRIAC is turned off. In the case of an incandescent lamp, which is essentially a resistive value, the passing current is higher than the sustaining level while the TRIAC is turned on. Thus, problems with the current through the TRIAC going below the sustaining level most likely do not occur when the TRIAC is connected to an incandescent lamp.
FIG. 1 depicts an example of a dimming circuit 100. A phase control circuit 106 is used to provide the phase control signal to turn on a TRIAC 104 at a controlled moment. To operate phase control circuit 106, a variable resistor R1 and a capacitor C1 are mounted in series with an incandescent lamp 102. Incandescent lamp 102 acts as a resistive load and offers a continuous path 108 to ground that allows current to flow through variable resistor R1 and capacitor C1 when the TRIAC is turned off. This allows a continuous flow of current that charges the capacitor in a desired amount of time that is set by variable resistor R1. The amount of time is set based on the conduction angle that is desired.
Electronic loads, such as light emitting diodes (LEDs) or fluorescent lamps, are replacing incandescent lamps. These electronic loads may not offer ideal conditions for dimmers using TRIACs. For example, the electronic loads do not intrinsically offer a continuous path to ground for the phase control circuit to charge the capacitor because the electronic loads do not provide a resistive load that allows current to flow to ground. Also, a sufficient sustaining current to keep the TRIAC turned on may not be provided.
One example uses dummy loads that supplement the missing conditions of the electronic loads to allow for proper functioning of the TRIAC. For example, a dummy load is added to allow the current to flow in a continuous path to ground. However, using the dummy load uses extra energy and also requires additional components for the system, which adds cost.